Diabetes is a disease which fails to sufficiently utilize glucose in the body. It follows that an increase in blood glucose level or chronic hyperglycemia is caused and various complications are induced. It is important to normalize blood glucose level in the treatment of diabetes. For that purpose, parenteral administration of insulin (an in vivo hormone which regulates blood glucose), oral administration of drugs and dietary therapy have now been carried out. Diabetes is classified into two major forms of type I diabetes and type II diabetes. Type I diabetes is the result of a deficiency of insulin, which is basically improved by administration of insulin. On the other hand, type II diabetes, which is insulin-nondependent diabetes, occurs in the face of normal or even elevated levels of insulin. This means that the tissue response to insulin is not normal. In the treatment of type II diabetes, oral administration of drugs which promote insulin secretion or repress absorption of sugar contained in the diet, parenteral administration of insulin and dietary therapy have been carried out. However, these are not fundamental methods for the treatment of diabetes, and patients frequently suffer from side effects and pains. Therefore, it has been earnestly desired to develop newer drugs that improve the pathosis of diabetes. In addition, a majority of cases of the type II diabetes are known to be associated with obesity, which suggests that the crisis of diabetes is closely related to the obesity. It is also known that, in a patient suffering from diabetes and obesity, diabetes is improved by eliminating obesity. Obesity is thought to be caused by accumulation of fat in the body, and in order to improve obesity, it is necessary to consume the accumulated fat. Recently, obesity or diabetes has become a problem in not only humans but also in pets due to excess nutrition and lack of exercise. Additionally, a method for decreasing fat and increasing lean meat has been desired for edible animals.
It is known that β-adrenergic receptors are divided into β1-, β2- and β3-subtypes. Stimulation of β1 receptor mainly causes an increase in heart rate. Stimulation of β2 receptor mainly causes bronchodilation and smooth muscle relaxation. Stimulation of β3 receptor mainly promotes lipolysis and energy consumption, by which a decrease in fat mass results. Accordingly, it is thought that compounds having β3 agonistic activity possess ant-obesity activity. In addition, it is reported that these compounds have anti-hyperglycemic activity in animal models of type II diabetes. These indicate that β3 agonists are useful in improving obesity in mammals and hyperglycemia in diabetes of mammals. The leading β3 agonists known at the present time include those described below, for example.
As one of the compounds, Ainsworth et al. disclose in Japanese Patent Kokai 56-5444 (JP 56-5444A) a compound (BRL 37344) of the following formula (III), its carboxylic acid methyl ester (BRL 35135) and their pharmaceutically acceptable salts.

These compounds have anti-obesity activity and anti-hyperglycemic activity. However, it is reported that side-effects, namely tremor caused by stimulation of β2 receptors, have been observed in clinical trials.
Bloom et al., in Japanese Patent Kokai 5-320153 (JP 05-320153A), disclose a compound of the following formula (IV) and a pharmaceutically acceptable salt thereof.

This compound has potent activity to β3 receptor in rodents and further has very high selectivity to β1 and β2 receptors. However, its efficacy in clinical trials has not been observed because of its weak activity to human β3 receptor.
Takahashi et al., in WO 96/35685, disclose a compound of the following formula (V) and a pharmaceutically acceptable salt thereof.

Guillaumet et al., in FR 2746395, disclose a compound of the following formula (VI) and its pharmaceutically acceptable salt thereof.

Although the activity to human β3 receptor is described in these cases, whether or not the compounds may have sufficiently useful activity and high selectivity is not indicated. Moreover, they do not mention the fact that the level of intrinsic activity is critical.
β3 Agonists are useful as anti-obesity agents or anti-hypoglycemic agents. However, the existing β3 agonists have disadvantages such that side effects will develop because they possess activity to β1 and β2 receptors, etc. other than β3 receptor or their activity to human β3 adrenergic receptor is weak despite of the activity to animal β3 receptor. In addition, one of the reasons that sufficient efficacy cannot be expected is believed to be that they are not full agonists but partial agonists, even if they have activity to human β3 receptor.
Under these circumstances, it has been desired to develop compounds having high activity and selectivity to human β3 receptor as well as having high intrinsic activity.